Compound master cylinder unit for hydraulic systems



June 23, 1953 c. E. DEARDORFF 2,642,720

COMPOUND MASTER CYLINDER UNIT FOR HYDRAULIC SYSTEMS Filed Feb. 21, 1950 4 I 7 2a 32 I25 14 I5 30 2O 9 5 12 I2 II 123 II 22 24 7 INVENTOR C. E. DEARDORFF ATTORNEY Patented June 23, 1953 COMPOUND MASTER CYLINDER UNIT FOR HYDRAULIC SYSTEMS Clinton E. Deardorfl', San Fernando, Calif., as-

signor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware 7 Application FebruaryZl, 1950, Serial No. 145,455

This invention relates to hydraulic systems in which manual or pedal actuation of a pump (master cylinder) unit delivers pressure fluid through a line to one or more remote motor cylinders for producing motion at the remote other hydraulic systems as well.

capable of producing.

that is simple and practicable.

follow of a specific embodiment.

der.

brake adjustments, willbe required.

2 Claims, (01. (SO-54.6)

of fluid at low: pressure, and is then capable of providing a, relatively small quantity of fluid at a much higher pressure. The large volume at low pressure suffices to fill the brake cylinders and move thebrake shoes out against the drums,

The higher pressure to During the booster When the booster The usual passages 54 and I5 5 point. A hydraulic brake system is a typical exwhereupon the higher pressure is developed to ample, and the invention will be described with increase the force that the shoes exert against reference thereto, although it has application to the drums. This result is obtained by providing, in the master cylinder unit, a large main pump An object of the invention is to increase the cy Wh iS C pa of delivering a large volumetric capacity of a master cylinder unit volume Of flu at 10W pressure- Without reducing the maximum pressure it is delivered through a check valve to the hydraulic line to fill the brakes.

Another object is to provide a master cylinder tighten the shoes against t e drums is developed unit capable, in response to a given actuating by a booster cy of much Smaller diameter force, of delivering a rapid flow of fluid at a low than the mai pump cylinder and which is actupressure, and a slower flow at a higher pressure. ated by a booster motel cylinder of large d am- Another object is to provide a master cylind eter. This booster motor cylinder is cut in autounit possessing the foregoing characteristics, matieally by a pressure p sive Va ve when the pressure in the main pump cylinder rises to Other more specific objects and features of the a predetermined V lu invention will appear from the description to .Operatwn, fluld flow from the brakelme b c to the main pump cylinder is prevented by a check In a conventional hydraulic brake system, the valvee the main hp P l sed to entire volume of fluid that is transmitted to the release t e brake, the fluid returning from th brake cylinders is delivered by the master cylin makes first retllms the Q {R and p hp The for e that can be applied to move the pistons to their retracted positions, the fluid piston of t master cylinder is limited by t being exhausted from the booster motor back into strength of th operator, and for a given force, the main p Cylinder either through the pr the maximum pressure that can be produced is 30, Sure responsive Valve 1 h ough a check valve determined by the diameter of the cylinder. By Provided for that p p making the diameter sufficiently small, a pressure pistons are fully cted, a Valve in t e booster of any desired magnitude can be obtained. Howpiston is opened to permit the remainder-9f the ever, reducing the diameter of the cylinder refluid in the lines to flew back t ugh the check duces the volume of fluid that can be discharged. valve t the main p cyli de In actual practice, the diameter of the cylinder Referring W t0 the w g: is a compromise between the maximum diameter F 1 is a longitudinal sectional v w thr ugh a thatwillproduce the desired pressure, and the compound master cylinder unit. in accordance minimum diameter that will deliver the quantity With the invention; and of fluid required. The volume of fluid that must 40 2 is a Sectional view similarto Fig- 1, but be delivered by the master cylinder is determined showing the parts in a difierent position of opby the adjustment of the brakes. If the brakes eration. v are adjusted as tightly as possible without drags The compound master cylinder unit disclosed in ging, the minimum amount of fluidis required. the drawing comprises the usual reservoir I0, On the other hand, as'the brakes wear, and the 5 main-pump cylinder H, and main pump piston clearance between the shoes and the drums in- I2. Thus the piston [2 comprises the usual pricreases, a larger volume of fluid is required to mary piston portion In and secondary piston move. the shoes out into engagement with the portion 12b, and contains a check valve l2c for drum. When the master cylinder capacity is permitting flow of fluid from the reservoir I0 into small, frequent brake adjustmentsare necessary. the main pumpcylinder during rapid retraction On the other hand, if the master. cylinder capac 0f the piston I2. ity can, be. made large, relatively infrequent are provided between reservoir l0 and the cylinder H. The present invention provides "a master cylin- The main pump cylinder I l is communicated by der that is capable of providing ;a large volume a pump discharge check valve 16 with a discharge This can be 3 passage I I that is adapted to be connected to the load (the usual brake line in a hydraulic brake system).

There is formed, integrally with the main pump cylinder H, a booster motor cylinder I8 and a booster pump cylinder I9, cylinder I8 containing a booster motor piston 20, and cylinder I9 containing a booster pump piston 2 I, which are formed as a single unit. The main pump cylinder I I is communicated with the booster motor cylinder I8 by a return-flow check valve 22 which permits flow from the cylinder I8 into the cylinder. I I' but prevents flow in the opposite direction. The booster pump cylinder I9 is communicated with the booster motor cylinder I8 by a passage 22' extending through the pistons 2I and and containing an auxiliary return-flow valve 24- which is held open by a projection 25 in the left end of the motor cylinder I8 when the piston 20- is in leftmost position.

'A booster control valve 21 communicates the main pump cylinder II with the booster motor cylinder I8 when the pressure is above a predetermined minimum, This valve 21 is in the form of a piston scaling in a small cylinder 28 which is vented to atmosphere by a vent 29 at its outer end and terminates at its inner end in a seat 30 which is in constant communication with the main pump cylinder H. The cylinder 28 is communicated intermediate its ends by a passage 32 with the booster motor cylinder I8. The valve 21 is urged against the seat 30 by a helical compression spring 34, the loading of which can be adjusted with a screw 35.

Fig. 1 shows the unit in inactive position, in which the main pump piston I2 is fully retracted to communicate the reservoir II) with the main pump cylinder II through the vent I:5, the valve 21 is closed, and the booster pistons 20 and 2| arein full retracted position. Now let it be assumed that the main. pump piston I2 is advanced to the right in response to movement of a brake pedal or other manually operable device. The piston displaces liquid from. the main pump cylinder II past the check valve I'6 into the discharge passage IT and thence to thebrakes (in a braking system) to fill the brake cylinders. During the filling period there will be relatively little reaction to the free flow of fluid from the discharge passage I1, and the pressure in the main pump cylinder I I will not rise high enough to open the valve 21.

However, when the brakes are filled, the pressure will rise in the discharge passage II andv in the cylinder II to a value sufiicient to open the valve 21 against the resistance of the spring 34, thereby permitting fluid to flow through the passage 32 into the booster motor cylinder I8. With the booster piston in the position shown in Fig. 1, this fluid could flow on through the passage 23 past the open valve 24. However, prior to the opening of the valve 21, the pistons 20 and 2.! move to the right a suflicient distance to carry the valve 24 clear of the projection 25 andpermit the valve to seat. This initial movement is produced by virtue of the fact that the face of piston 20 has a much larger area than the face of piston 2I, so that the same pressure applied to both faces will cause the piston to move to the right. Since the auxiliary pump cylinder I9 is permanently connected to the discharge passage II, the pressure in the cylinder I9 and in the cylinder IB rises with the pressure in the discharge line I! prior to the opening of the valve2l.

For the reasons given, the pistons 20 and 2| have moved sufficiently to permit closure of the valve 24 prior to the time when the valve 2! opened. Therefore, after the opening of the valve 21, fluid flows from the main pump cylinder Il into the booster motor cylinder I8 and moves the booster motor piston 20 and the booster pump piston H to the right, forcing the fluid trapped in the cylinder I9 into the discharge passage II. By virtue of the fact that the face of piston 2| is-much smaller than the face of the main pump piston I-2,v a. substantially higher pressure can be produced. in the discharge passage I'I after the valve 21 opens than it was possible to produce with the main cylinder II and main piston I2 alone.

When the maximum force has been applied to the main pump piston I2, the mechanism may be in the condition shown in Fig. 2. It will be noted that the valve 21 remains open as long as the pressure in the main pump cylinder II remains above a predetermined value.

When the force is removed from the main pump piston I2 the pressure in the main pump cylinder drops, and fluid flows back into the unit from the brakes through the discharge passage I1. Such return flow of fluid is initially into the cylinder I9, since both the valve I6 and 24 are closed. This returns the pistons 2I and 20 and displaces fluid from the motor cylinder I.8 back into the pump cylinder II either through the passage 32 and past the valve 21 (as long as the latter remains open) or past the check valve 22. When the piston 20 returns to its normal position, the projection 25 opens the valve 24, and, thereafter, fluid returning from the brakes through the passage I1 flows through the cylinder I9, the passage 23, past the open valve 24 into the cylinder I8, and thence past the check valve 22 into the main pump cylinder II. This restores the apparatus to the normal position as shown in Fig. 1 and completes a cycle of operation.

Because of the large diameter of the main pump cylinder II, only a. fraction of the full stroke of the main pump piston I2 suflices to fill the brake cylinders and move the shoes into contact with the drum even when the brakes are in relatively loose adjustment. The additional movement of the main piston, after the brakes have contacted the drums and the valve 21 has opened, is independent of the brake adjustment and is relatively small, since brake shoes move very little in response to further increase in P s ure af they are against the drums.

A conventional master cylinder capable of developing the-same pressure would have to employ a pump piston of the same, small diameter as the'booster piston 2 I, and obviously it would have to have a much longer stroke than the large piston I2 to have the same filling capacity.

Although for the purpose of explaining the invention, a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do notdesire to be limited to the exact details shown and described.

I claim:

1. Apparatus for supplying pressure fluid to a hydraulic system comprising: a main pump cylinder containing a main pump piston normally retracted and adapted to be advanced by external force to discharge fluid from said main pump cylinder; a discharge passage adapted to be connected to a load line, and a pump discharge check valve connecting said main pump cylinder to said discharge passage for flow from said cylinder to said passage; a booster motor cylinder connected to said main pump cylinder by a return-flow check valve for permitting flow from said booster motor cylinder to said main pump cylinder; a normally retracted booster motor piston in said booster motor cylinder adapted to be advanced by fluid flow into said booster motor cylinder; a booster pump cylinder of smaller bore than said booster motor cylinderand connected to said discharge passage; a normally retracted booster pump piston in said booster pump cylinder and means for advancing it to expel fluid from said booster pump cylinder into said discharge passage in response to advance of said booster motor piston; a pressure responsive booster pump control valve communicating said main pump cylinder with said booster motor cylinder in response to pressures in said main pump cylinder above a predetermined value; a passage intercommunicating said booster motor and booster pump cylinders, and an auxiliary return flow valve in said last mentioned passage for blocking flow from said booster pump cylinder to said booster motor cylinder except when said booster pistons are in their retracted positions; said auxiliary return flow valve consisting of a check valve directed to permit flow from said booster motor cylinder to said booster pump cylinder in all positions of said booster pistons, and stop means for engaging said check valve and opening it for fluid flow therethrough in both directions in response to movement of said booster pistons into retracted position.

to said main pump cylinder by a return flow 2. Apparatus for supplying pressure fluid to a check valve 'for permitting flow from saidbooster motor cylinder to said main pump cylinder; a normally retracted booster motor piston in said booster motor cylinder adapted to be advanced by fluid flow into said booster motor cylinder; a booster pump cylinder of smaller bore than said booster motor cylinder and connected to said discharge passage; a normally retracted booster pump piston in said booster pump cylinder and meansfor advancing it to expel fluid from said booster pump cylinder into said discharge passage in response to advance of said booster motor piston; a pressure responsive booster pump control valve communicating said main pump cylinder with said booster motor cylinder in response to pressures in said main pump cylinder exceeding atmospheric pressure by a predetermined fixed value, said booster control valve means comprising a piston element having one face exposed to the pressure fluid in said main pump cylinder and an opposite face exposed to atmospheric pressure, and spring means acting on said piston element in opposition to pressure forces on said one face; passage means including a normally closed auxiliary return flow valve communicating said booster pump cylinder and said discharge passage with said booster motor cylinder; and means responsive to the position of said booster pistons for opening said auxiliary valve when said booster pistons are in their retracted positions. 1

CLINTON E. DEARDORFF.

References Cited in the file of this patent UNITED STATES PATENTS Cousino Oct. 26, 1948 

